Let me sart off by answering your question about do I think something is wrong with a 12 year old vehicle with over 100k miles. HECK YEAH there is stuff wrong with it LOL. The big question is what exactly is wrong with it. I would not pay that much for it but 5K sounds about right for an average market price. I would try to allow enough cash in the deal to change all the fluids Coolant/Brake fluid/Differentials/Transfer case/power steering fluid/Transmission fluid to make sure you get another 100k fairly trouble free miles. Do you think your ole buddy would do you a solid and have all that done for you before you pick it up and still keep the price at 5k?
Just curious what you base this off of? We don't have any clue about the maintenance history of it. If fluids and filters are changed, and average maintenance has been kept up. Why would you assume there HAS TO be something wrong with it? This just sounds like something you would say about a car from the 80s. I think modern, even 20 year old automotive technology is better than that. Maybe not for all makes, but my GM vehicles have been great. In 240K miles the ONLY thing that went wrong was a plastic heater hose coupling. Sure, I've replaced the battery, alternator, belts, tires, waterpump, filters, fluids, but that's all standard maintenance.